A wide variety of applications require the moving or pumping of fluids. One large category of applications is the moving of fluids, either gaseous or liquid, to transfer thermal energy from one location to another location, such as for cooling or heating. Another category of applications is the moving of fluids as part of a chemical reaction process, such as supplying oxygen or air to the cathode of a fuel cell. Still another category of applications is for supplying a fluid to a device at elevated pressure, such as an air pump for pressurizing vehicle tires.
Many implementations of pumping devices have been developed to address these various applications. The most common and prevalent of these devices use electrical energy as the power source to drive mechanical motion to accomplish the pumping action. One typical example is an impeller fan having multiple blades that are driven in a rotary fashion by an electric motor. Fans are typically capable of moving large fluid quantities at a low increase in the fluid kinetic energy and pressure. Centrifugal blowers are capable of moving large fluid quantities at low to intermediate pressures. Compressors are similar devices that typically have multiple stages of rotating blades and are capable of pumping smaller quantities of fluids at relatively high pressures. Rotary vane pumps use an eccentrically mounted rotor containing sliding vanes to continuously pump fluid at moderate pressures. Gear pumps use multiple rotating gears to continuously pump fluid from the low pressure inlet to an elevated pressure outlet. Reciprocating pumps driven by an electric motor typically convert the rotating action of a shaft to a reciprocating linear motion, particularly employing a crankshaft to drive a piston or diaphragm actuator. Reciprocating pumps typically use check valves or similar devices to prevent reverse flow of the pumped fluid back into the pump chamber once it has been biased in a predetermined, desired flow direction. Linear pumps typically use an electric solenoid drive or other linear electric actuator in a free piston design to create pumping action by moving a piston in a linear motion.
Impeller fans are well-suited for a wide variety of cooling and fluid-movement applications in which the pressure rise requirements are very small, typically 1″ H2O (250 Pa) or less. Fans typically exhibit pumping efficiencies of 50-70%. For applications that require higher pressure rise values, other pumping devices should be considered. To this end, centrifugal blowers can have higher pressure capacity, typically up to 10″ H2O (2500 Pa), though the flow rate at maximum pressure approaches zero and the efficiency is low. Compressors are well-suited for low-flow, high-pressure rise applications. Compressors typically provide pressure rise values from tens of psi to hundreds of psi (0.1-1 MPa and higher). Compressors are generally not employed for cooling, heating, or fluid movement applications.
Rotary vane, gear, and reciprocating pumps are well-suited for intermediate pressure applications that do not require large volumetric flow rates. Rotary vane and gear pumps use sliding surfaces in conjunction with rotating motion. Friction and wear are disadvantages associated with the sliding surfaces. Reciprocating pumps traditionally employ a crankshaft mechanism to convert the rotary motion of the electric drive motor to linear motion of the actuator. Reciprocating pumps typically require lubrication, though use of a diaphragm actuator separates the lubricant from the pumping fluid.
Linear pumps are suitable for both low and intermediate pressure applications. A common limitation on linear pumps with solenoid actuation is low frequency operation which dictates that the pumps be constructed to a large size for a given flow rate. Some reciprocating pump designs incorporate a mechanical return spring to allow operation at increased frequency. Typically, the electrical drive efficiency of linear pumps is low. Current pump technologies have numerous limitations for applications requiring compact size, light weight, low power, and intermediate pressures. Impeller fans exhibit inadequate pressure capabilities. Compressors are heavy and are inappropriate at intermediate pressures. Blowers can provide intermediate pressure at moderate flow rates, though their efficiency is low, and their size and weight are frequently greater than that which is desired for compact applications. Rotary vane pumps and gear pumps exhibit wear issues associated with the sliding parts and a size and weight that may be excessive for the desired application. Reciprocating pumps employ a crank mechanism that experiences wear and generally requires lubrication. In the case of piston pumps, the lubricant also has the potential for contaminating the fluid which is being pumped. Reciprocating pumps usually have a size and weight that exceeds the desired parameters for compact applications.
In addition to the electrically-powered pumping devices discussed above, pumping devices using energy from combustion, either directly as in combustion driven devices, or indirectly such as in steam engine or Stirling engine devices, have been developed. These include free piston pump devices. These devices are typically large and heavy, and not well-suited for low and intermediate pressure applications. These devices are also not suitable for many applications requiring a small size, since they require heat transfer surfaces and cooling flow for heat rejection. They are also generally not suitable for indoor use since they require exhaust ducting and a fuel supply
It is, thus, desirable to provide a pump arrangement that can produce a large airflow at intermediate to high pressures in a compact and lightweight assembly. This pump should allow for variable flow and pressure control and relatively quiet operation. The pump arrangement should handle both gasses and liquids, and should be adaptable to a variety of applications including those employing connected conduits and submerged applications. Moreover, the pump should exhibit relatively low wear with few wear parts, and should operate with minimal lubrication or potential for contamination of the driven fluid (gas or liquid). It is further desirable to provide various mechanical improvements to both pumps and other free-piston drive systems such as Miniature Internal Combustion Engines (described further below).